1. Field of the Invention
This invention relates generally to the field of analytical chemistry, and more specifically to a method and apparatus for the digestion of organic matter prior to analysis. Apparatus used in the method includes a specially designed microwave oven system for containing and treating acid fumes evolved and for controlling precisely the rate at which such digestion occurs.
2. Description of the Prior Art
Numerous processes for the digestion of organic matter prior to metals or nitrogen analyses are known in the art. The problems associated therewith are also well known. Wet ashing processes and problems are described most comprehensively by T. T. Gorsuch in The Analyst, (1959), and in his book entitled: "The Destruction of Organic Matter", Pergamon Press, New York, New York, 1970. The Kjeldahl digestion has been discussed comprehensively in the book by R. B. Bradstreet entitled: "The Kjeldahl Method for Organic Nitrogen", Academic Press, N.Y., 1965.
The "wet ashing" methods have gained greatest acceptance among investigators interested in trace metals analyses, and the Kjeldahl digestion is almost universally used prior to nitrogen determinations. The wet digestion methods suffer from the disadvantages of requiring close and constant operator attention, the need for special hoods to handle the acid fumes (especially perchloric acid) safely, and the danger of explosion if established procedures are not strictly followed. Also, in certain cases where speed is required, such as in neutron activation analysis, the elapsed time can also be a limitation.
The primary advantage of utilizing the present invention is the speed with which the digestion can be carried out. Ashings which normally require 1 - 2 hours with nearly constant operator attention can be done in 5 - 15 minutes with little or no operator attention.
Microwave ovens for the cooking of foods are well known in the art, as typified by the patent to Hall, U.S. Pat. No. 2,500,676, entitled: HEATING APPARATUS. Such ovens for cooking have also been designed with flow-through ventilation systems, as shown in the patent to Javes, et al., U.S. Pat. No. 3,654,417 entitled: MICROWAVE OVEN INCLUDING AIR FLOW SYSTEM.
Microwave energy has also been used for producing and controlling chemical reactions for specific purposes, as shown by the patent to Jacobs, U.S. Pat. No. 3,294,879, entitled: METHOD FOR MAKING POLYURETHANE FOAM.
None of the apparatus described above, or related thereto are designed for the destruction of organic matter, and particularly, no existing microwave apparatus is known that is capable of withstanding the corrosive environment created by the corrosive acid fumes generated in the digestion processes.